FIG. 10 is a conceptual view illustrating an inverter for motor control as one example of a module using a conventional semiconductor device. In using a semiconductor device (power device) adapted to control a motor 1 as an IC or a module as shown in FIG. 10, it has been technically difficult to integrate a control circuit 3 comprising, for example, a low-voltage control/logic semiconductor circuit to be driven by a low-voltage power supply 2 and power switching devices 5H and 5L adapted to handle a high-voltage large current supplied from a high-voltage power supply 4 into one chip or to pack these circuit and devices into the same package. For this reason, small number of such ICs or modules that can be widely used for industrial purposes has been reported. Power ICs and modules fabricated by the current Si semiconductor technology are formed through a quite complicated process fully utilizing an isolation technique for electrically isolating low-voltage devices from high-voltage devices.
In a semiconductor device called “intelligent power module” (IPM) (see non-patent document 1 for example), in particular, a gate drive circuit 6, which is associated with the high-side power switching device 5H of the power switching devices (IGBTs, MOSFETs or the like) included in the inverter adapted to control the motor 1 or the like, needs to operate in a high-potential condition floating relative to the ground potential and, hence, a high-potential floating power supply 7 is also needed. This is because the potential of the connecting portion between the high-side power switching device 5H and the low-side power switching device 5L which are connected to the load fluctuates constantly depending upon the conditions of the power switching devices and, hence, the power switching device 5H, which is on the high side relative to such a fluctuating potential, needs to be applied with a gate potential for switching control. To this end, a level shift technique is needed such as to allow signals relative to the ground potential used as a reference that are fed from the control circuit 3 to be transferred to the gate drive circuit 6 in a high-potential floating condition.    Patent document 1: Japanese Patent Laid-Open Publication No. HEI 10-027853    Patent document 2: Japanese Patent Laid-Open Publication No. HEI 06-260601    Patent document 3: Japanese Patent Laid-Open Publication No. HEI 08-335863    Patent document 4: Japanese Patent Laid-Open Publication No. 2000-286391    Non-patent document 1: “POWER DEVICE•POWER IC HANDBOOK”, CORONA PUBLISHING CO., LTD., edited by high-performance and high-capability power device and power IC research expert committee of The institute of Electrical Engineers of Japan, P. 218